This invention relates to dynamoelectric machines with a radial path, air-cooled rotor in which the rotor is cooled by a gas such as air that flows axially into the rotor and radially out through passages in the slot conductors.
In former machines of a known type, the rotor cooling gas enters an axial duct at the bottom of each coil slot. The axial duct serves as a manifold from which the gas is vented through a plurality of radially extending vents that go through the slot conductors. Practical machine construction has required having an insulative cell lining each coil slot and extending somewhat, such as one inch, from the ends of the rotor to ensure integrity of the insulation. A channel member is disposed at the bottom of the slots adjacent the cell and also extends somewhat from the ends of the rotor. The edges of the protruding portions of the ventilating channel and cell have an adverse effect on the flow through the channel because they represent a relatively sharp edged protruding entrance which produces a high inlet pressure drop that results in less than desirable flow rates and hence higher temperatures of the rotor and the conductors therein. Air flow can be improved by external blowers mounted on the shaft that act as fans producing greater flow into the ventilating channels. The external blowers contribute to an increase in machine size, weight and airborne noise levels which is undesirable.
In accordance with the present invention, the basic described structure including a slot cell and channel that extend from the face of the rotor is modified by the provision of a fairing that is disposed against the rotor end face adjacent the protruding cell and channel and shaped to fit closely around the extended portions of the cell and channel and to have a smooth flow transition region that introduces coolant gas into the channel during rotation of the rotor with a low inlet pressure drop, found to be reduced by a factor of about 20 as compared to that of the former structure. A consequent increase in the flow rate of air through the rotor and better cooling results so a higher machine rating can be achieved. The use of the fairing to modify the pressure drop at the channel inlet can improve the machine rating and eliminate or reduce the need for external blowers. Machine rating per unit weight (KW/lb.) can therefore be improved by up to about three or four percent which is particularly significant in certain applications such as for shipboard use.
The channel inlet fairing also improves the facility with which the respective channels can be individually orificed for thermal balancing of the rotor slot conductors. By "orificing" is meant the practice of partially blocking certain channels found by tests to have greater cooling than others. The balancing permits all channels, and hence all parts of the rotor, to be equally cooled and lessens the structure-borne noise produced by the machine. By this invention, the fairing provides a surface on which a blocking element can be readily fastened, partially covering the channel opening to the extent necessary to achieve the desired balance. In the past, it has been less convenient to mount a blocking element at the channel opening.